The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1989, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD$");
   39 
   40 #include "opt_ktrace.h"
   41 #include "opt_mac.h"
   42 
   43 #include <sys/param.h>
   44 #include <sys/systm.h>
   45 #include <sys/sysproto.h>
   46 #include <sys/eventhandler.h>
   47 #include <sys/filedesc.h>
   48 #include <sys/kernel.h>
   49 #include <sys/kthread.h>
   50 #include <sys/sysctl.h>
   51 #include <sys/lock.h>
   52 #include <sys/malloc.h>
   53 #include <sys/mutex.h>
   54 #include <sys/proc.h>
   55 #include <sys/pioctl.h>
   56 #include <sys/resourcevar.h>
   57 #include <sys/sched.h>
   58 #include <sys/syscall.h>
   59 #include <sys/vmmeter.h>
   60 #include <sys/vnode.h>
   61 #include <sys/acct.h>
   62 #include <sys/mac.h>
   63 #include <sys/ktr.h>
   64 #include <sys/ktrace.h>
   65 #include <sys/unistd.h> 
   66 #include <sys/sx.h>
   67 #include <sys/signalvar.h>
   68 
   69 #include <vm/vm.h>
   70 #include <vm/pmap.h>
   71 #include <vm/vm_map.h>
   72 #include <vm/vm_extern.h>
   73 #include <vm/uma.h>
   74 
   75 #include <machine/critical.h>
   76 
   77 #ifndef _SYS_SYSPROTO_H_
   78 struct fork_args {
   79         int     dummy;
   80 };
   81 #endif
   82 
   83 static int forksleep; /* Place for fork1() to sleep on. */
   84 
   85 /*
   86  * MPSAFE
   87  */
   88 /* ARGSUSED */
   89 int
   90 fork(td, uap)
   91         struct thread *td;
   92         struct fork_args *uap;
   93 {
   94         int error;
   95         struct proc *p2;
   96 
   97         error = fork1(td, RFFDG | RFPROC, 0, &p2);
   98         if (error == 0) {
   99                 td->td_retval[0] = p2->p_pid;
  100                 td->td_retval[1] = 0;
  101         }
  102         return (error);
  103 }
  104 
  105 /*
  106  * MPSAFE
  107  */
  108 /* ARGSUSED */
  109 int
  110 vfork(td, uap)
  111         struct thread *td;
  112         struct vfork_args *uap;
  113 {
  114         int error;
  115         struct proc *p2;
  116 
  117         error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
  118         if (error == 0) {
  119                 td->td_retval[0] = p2->p_pid;
  120                 td->td_retval[1] = 0;
  121         }
  122         return (error);
  123 }
  124 
  125 /*
  126  * MPSAFE
  127  */
  128 int
  129 rfork(td, uap)
  130         struct thread *td;
  131         struct rfork_args *uap;
  132 {
  133         struct proc *p2;
  134         int error;
  135 
  136         /* Don't allow kernel-only flags. */
  137         if ((uap->flags & RFKERNELONLY) != 0)
  138                 return (EINVAL);
  139 
  140         error = fork1(td, uap->flags, 0, &p2);
  141         if (error == 0) {
  142                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  143                 td->td_retval[1] = 0;
  144         }
  145         return (error);
  146 }
  147 
  148 int     nprocs = 1;             /* process 0 */
  149 int     lastpid = 0;
  150 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  151     "Last used PID");
  152 
  153 /*
  154  * Random component to lastpid generation.  We mix in a random factor to make
  155  * it a little harder to predict.  We sanity check the modulus value to avoid
  156  * doing it in critical paths.  Don't let it be too small or we pointlessly
  157  * waste randomness entropy, and don't let it be impossibly large.  Using a
  158  * modulus that is too big causes a LOT more process table scans and slows
  159  * down fork processing as the pidchecked caching is defeated.
  160  */
  161 static int randompid = 0;
  162 
  163 static int
  164 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  165 {
  166         int error, pid;
  167 
  168         error = sysctl_wire_old_buffer(req, sizeof(int));
  169         if (error != 0)
  170                 return(error);
  171         sx_xlock(&allproc_lock);
  172         pid = randompid;
  173         error = sysctl_handle_int(oidp, &pid, 0, req);
  174         if (error == 0 && req->newptr != NULL) {
  175                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  176                         pid = PID_MAX - 100;
  177                 else if (pid < 2)                       /* NOP */
  178                         pid = 0;
  179                 else if (pid < 100)                     /* Make it reasonable */
  180                         pid = 100;
  181                 randompid = pid;
  182         }
  183         sx_xunlock(&allproc_lock);
  184         return (error);
  185 }
  186 
  187 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  188     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  189 
  190 int
  191 fork1(td, flags, pages, procp)
  192         struct thread *td;
  193         int flags;
  194         int pages;
  195         struct proc **procp;
  196 {
  197         struct proc *p1, *p2, *pptr;
  198         uid_t uid;
  199         struct proc *newproc;
  200         int ok, trypid;
  201         static int curfail, pidchecked = 0;
  202         static struct timeval lastfail;
  203         struct filedesc *fd;
  204         struct filedesc_to_leader *fdtol;
  205         struct thread *td2;
  206         struct ksegrp *kg2;
  207         struct sigacts *newsigacts;
  208         int error;
  209 
  210         /* Can't copy and clear. */
  211         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  212                 return (EINVAL);
  213 
  214         p1 = td->td_proc;
  215 
  216         /*
  217          * Here we don't create a new process, but we divorce
  218          * certain parts of a process from itself.
  219          */
  220         if ((flags & RFPROC) == 0) {
  221                 vm_forkproc(td, NULL, NULL, flags);
  222 
  223                 /*
  224                  * Close all file descriptors.
  225                  */
  226                 if (flags & RFCFDG) {
  227                         struct filedesc *fdtmp;
  228                         fdtmp = fdinit(td->td_proc->p_fd);
  229                         fdfree(td);
  230                         p1->p_fd = fdtmp;
  231                 }
  232 
  233                 /*
  234                  * Unshare file descriptors (from parent).
  235                  */
  236                 if (flags & RFFDG) 
  237                         fdunshare(p1, td);
  238                 *procp = NULL;
  239                 return (0);
  240         }
  241 
  242         /*
  243          * Note 1:1 allows for forking with one thread coming out on the
  244          * other side with the expectation that the process is about to
  245          * exec.
  246          */
  247         if (p1->p_flag & P_HADTHREADS) {
  248                 /*
  249                  * Idle the other threads for a second.
  250                  * Since the user space is copied, it must remain stable.
  251                  * In addition, all threads (from the user perspective)
  252                  * need to either be suspended or in the kernel,
  253                  * where they will try restart in the parent and will
  254                  * be aborted in the child.
  255                  */
  256                 PROC_LOCK(p1);
  257                 if (thread_single(SINGLE_NO_EXIT)) {
  258                         /* Abort. Someone else is single threading before us. */
  259                         PROC_UNLOCK(p1);
  260                         return (ERESTART);
  261                 }
  262                 PROC_UNLOCK(p1);
  263                 /*
  264                  * All other activity in this process
  265                  * is now suspended at the user boundary,
  266                  * (or other safe places if we think of any).
  267                  */
  268         }
  269 
  270         /* Allocate new proc. */
  271         newproc = uma_zalloc(proc_zone, M_WAITOK);
  272 #ifdef MAC
  273         mac_init_proc(newproc);
  274 #endif
  275         knlist_init(&newproc->p_klist, &newproc->p_mtx);
  276 
  277         /* We have to lock the process tree while we look for a pid. */
  278         sx_slock(&proctree_lock);
  279 
  280         /*
  281          * Although process entries are dynamically created, we still keep
  282          * a global limit on the maximum number we will create.  Don't allow
  283          * a nonprivileged user to use the last ten processes; don't let root
  284          * exceed the limit. The variable nprocs is the current number of
  285          * processes, maxproc is the limit.
  286          */
  287         sx_xlock(&allproc_lock);
  288         uid = td->td_ucred->cr_ruid;
  289         if ((nprocs >= maxproc - 10 &&
  290             suser_cred(td->td_ucred, SUSER_RUID) != 0) ||
  291             nprocs >= maxproc) {
  292                 error = EAGAIN;
  293                 goto fail;
  294         }
  295 
  296         /*
  297          * Increment the count of procs running with this uid. Don't allow
  298          * a nonprivileged user to exceed their current limit.
  299          */
  300         PROC_LOCK(p1);
  301         ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  302                 (uid != 0) ? lim_cur(p1, RLIMIT_NPROC) : 0);
  303         PROC_UNLOCK(p1);
  304         if (!ok) {
  305                 error = EAGAIN;
  306                 goto fail;
  307         }
  308 
  309         /*
  310          * Increment the nprocs resource before blocking can occur.  There
  311          * are hard-limits as to the number of processes that can run.
  312          */
  313         nprocs++;
  314 
  315         /*
  316          * Find an unused process ID.  We remember a range of unused IDs
  317          * ready to use (from lastpid+1 through pidchecked-1).
  318          *
  319          * If RFHIGHPID is set (used during system boot), do not allocate
  320          * low-numbered pids.
  321          */
  322         trypid = lastpid + 1;
  323         if (flags & RFHIGHPID) {
  324                 if (trypid < 10)
  325                         trypid = 10;
  326         } else {
  327                 if (randompid)
  328                         trypid += arc4random() % randompid;
  329         }
  330 retry:
  331         /*
  332          * If the process ID prototype has wrapped around,
  333          * restart somewhat above 0, as the low-numbered procs
  334          * tend to include daemons that don't exit.
  335          */
  336         if (trypid >= PID_MAX) {
  337                 trypid = trypid % PID_MAX;
  338                 if (trypid < 100)
  339                         trypid += 100;
  340                 pidchecked = 0;
  341         }
  342         if (trypid >= pidchecked) {
  343                 int doingzomb = 0;
  344 
  345                 pidchecked = PID_MAX;
  346                 /*
  347                  * Scan the active and zombie procs to check whether this pid
  348                  * is in use.  Remember the lowest pid that's greater
  349                  * than trypid, so we can avoid checking for a while.
  350                  */
  351                 p2 = LIST_FIRST(&allproc);
  352 again:
  353                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  354                         PROC_LOCK(p2);
  355                         while (p2->p_pid == trypid ||
  356                             (p2->p_pgrp != NULL &&
  357                             (p2->p_pgrp->pg_id == trypid ||
  358                             (p2->p_session != NULL &&
  359                             p2->p_session->s_sid == trypid)))) {
  360                                 trypid++;
  361                                 if (trypid >= pidchecked) {
  362                                         PROC_UNLOCK(p2);
  363                                         goto retry;
  364                                 }
  365                         }
  366                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  367                                 pidchecked = p2->p_pid;
  368                         if (p2->p_pgrp != NULL) {
  369                                 if (p2->p_pgrp->pg_id > trypid &&
  370                                     pidchecked > p2->p_pgrp->pg_id)
  371                                         pidchecked = p2->p_pgrp->pg_id;
  372                                 if (p2->p_session != NULL &&
  373                                     p2->p_session->s_sid > trypid &&
  374                                     pidchecked > p2->p_session->s_sid)
  375                                         pidchecked = p2->p_session->s_sid;
  376                         }
  377                         PROC_UNLOCK(p2);
  378                 }
  379                 if (!doingzomb) {
  380                         doingzomb = 1;
  381                         p2 = LIST_FIRST(&zombproc);
  382                         goto again;
  383                 }
  384         }
  385         sx_sunlock(&proctree_lock);
  386 
  387         /*
  388          * RFHIGHPID does not mess with the lastpid counter during boot.
  389          */
  390         if (flags & RFHIGHPID)
  391                 pidchecked = 0;
  392         else
  393                 lastpid = trypid;
  394 
  395         p2 = newproc;
  396         p2->p_state = PRS_NEW;          /* protect against others */
  397         p2->p_pid = trypid;
  398         LIST_INSERT_HEAD(&allproc, p2, p_list);
  399         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  400         PROC_LOCK(p2);
  401         PROC_LOCK(p1);
  402         sx_xunlock(&allproc_lock);
  403 
  404         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  405             __rangeof(struct proc, p_startcopy, p_endcopy));
  406         PROC_UNLOCK(p1);
  407 
  408         bzero(&p2->p_startzero,
  409             __rangeof(struct proc, p_startzero, p_endzero));
  410 
  411         p2->p_ucred = crhold(td->td_ucred);
  412         PROC_UNLOCK(p2);
  413 
  414         /*
  415          * Malloc things while we don't hold any locks.
  416          */
  417         if (flags & RFSIGSHARE)
  418                 newsigacts = NULL;
  419         else
  420                 newsigacts = sigacts_alloc();
  421 
  422         /*
  423          * Copy filedesc.
  424          */
  425         if (flags & RFCFDG) {
  426                 fd = fdinit(p1->p_fd);
  427                 fdtol = NULL;
  428         } else if (flags & RFFDG) {
  429                 fd = fdcopy(p1->p_fd);
  430                 fdtol = NULL;
  431         } else {
  432                 fd = fdshare(p1->p_fd);
  433                 if (p1->p_fdtol == NULL)
  434                         p1->p_fdtol =
  435                                 filedesc_to_leader_alloc(NULL,
  436                                                          NULL,
  437                                                          p1->p_leader);
  438                 if ((flags & RFTHREAD) != 0) {
  439                         /*
  440                          * Shared file descriptor table and
  441                          * shared process leaders.
  442                          */
  443                         fdtol = p1->p_fdtol;
  444                         FILEDESC_LOCK_FAST(p1->p_fd);
  445                         fdtol->fdl_refcount++;
  446                         FILEDESC_UNLOCK_FAST(p1->p_fd);
  447                 } else {
  448                         /* 
  449                          * Shared file descriptor table, and
  450                          * different process leaders 
  451                          */
  452                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  453                                                          p1->p_fd,
  454                                                          p2);
  455                 }
  456         }
  457         /*
  458          * Make a proc table entry for the new process.
  459          * Start by zeroing the section of proc that is zero-initialized,
  460          * then copy the section that is copied directly from the parent.
  461          */
  462         td2 = FIRST_THREAD_IN_PROC(p2);
  463         kg2 = FIRST_KSEGRP_IN_PROC(p2);
  464 
  465         /* Allocate and switch to an alternate kstack if specified. */
  466         if (pages != 0)
  467                 vm_thread_new_altkstack(td2, pages);
  468 
  469         PROC_LOCK(p2);
  470         PROC_LOCK(p1);
  471 
  472         bzero(&td2->td_startzero,
  473             __rangeof(struct thread, td_startzero, td_endzero));
  474         bzero(&kg2->kg_startzero,
  475             __rangeof(struct ksegrp, kg_startzero, kg_endzero));
  476 
  477         bcopy(&td->td_startcopy, &td2->td_startcopy,
  478             __rangeof(struct thread, td_startcopy, td_endcopy));
  479         bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy,
  480             __rangeof(struct ksegrp, kg_startcopy, kg_endcopy));
  481 
  482         td2->td_sigstk = td->td_sigstk;
  483         td2->td_sigmask = td->td_sigmask;
  484 
  485         /*
  486          * Duplicate sub-structures as needed.
  487          * Increase reference counts on shared objects.
  488          */
  489         p2->p_flag = 0;
  490         if (p1->p_flag & P_PROFIL)
  491                 startprofclock(p2);
  492         mtx_lock_spin(&sched_lock);
  493         p2->p_sflag = PS_INMEM;
  494         /*
  495          * Allow the scheduler to adjust the priority of the child and
  496          * parent while we hold the sched_lock.
  497          */
  498         sched_fork(td, td2);
  499 
  500         mtx_unlock_spin(&sched_lock);
  501         td2->td_ucred = crhold(p2->p_ucred);    /* XXXKSE */
  502 
  503         pargs_hold(p2->p_args);
  504 
  505         if (flags & RFSIGSHARE) {
  506                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  507         } else {
  508                 sigacts_copy(newsigacts, p1->p_sigacts);
  509                 p2->p_sigacts = newsigacts;
  510         }
  511         if (flags & RFLINUXTHPN) 
  512                 p2->p_sigparent = SIGUSR1;
  513         else
  514                 p2->p_sigparent = SIGCHLD;
  515 
  516         p2->p_textvp = p1->p_textvp;
  517         p2->p_fd = fd;
  518         p2->p_fdtol = fdtol;
  519 
  520         /*
  521          * p_limit is copy-on-write.  Bump its refcount.
  522          */
  523         p2->p_limit = lim_hold(p1->p_limit);
  524 
  525         pstats_fork(p1->p_stats, p2->p_stats);
  526 
  527         PROC_UNLOCK(p1);
  528         PROC_UNLOCK(p2);
  529 
  530         /* Bump references to the text vnode (for procfs) */
  531         if (p2->p_textvp)
  532                 vref(p2->p_textvp);
  533 
  534         /*
  535          * Set up linkage for kernel based threading.
  536          */
  537         if ((flags & RFTHREAD) != 0) {
  538                 mtx_lock(&ppeers_lock);
  539                 p2->p_peers = p1->p_peers;
  540                 p1->p_peers = p2;
  541                 p2->p_leader = p1->p_leader;
  542                 mtx_unlock(&ppeers_lock);
  543                 PROC_LOCK(p1->p_leader);
  544                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  545                         PROC_UNLOCK(p1->p_leader);
  546                         /*
  547                          * The task leader is exiting, so process p1 is
  548                          * going to be killed shortly.  Since p1 obviously
  549                          * isn't dead yet, we know that the leader is either
  550                          * sending SIGKILL's to all the processes in this
  551                          * task or is sleeping waiting for all the peers to
  552                          * exit.  We let p1 complete the fork, but we need
  553                          * to go ahead and kill the new process p2 since
  554                          * the task leader may not get a chance to send
  555                          * SIGKILL to it.  We leave it on the list so that
  556                          * the task leader will wait for this new process
  557                          * to commit suicide.
  558                          */
  559                         PROC_LOCK(p2);
  560                         psignal(p2, SIGKILL);
  561                         PROC_UNLOCK(p2);
  562                 } else
  563                         PROC_UNLOCK(p1->p_leader);
  564         } else {
  565                 p2->p_peers = NULL;
  566                 p2->p_leader = p2;
  567         }
  568 
  569         sx_xlock(&proctree_lock);
  570         PGRP_LOCK(p1->p_pgrp);
  571         PROC_LOCK(p2);
  572         PROC_LOCK(p1);
  573 
  574         /*
  575          * Preserve some more flags in subprocess.  P_PROFIL has already
  576          * been preserved.
  577          */
  578         p2->p_flag |= p1->p_flag & P_SUGID;
  579         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  580         SESS_LOCK(p1->p_session);
  581         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  582                 p2->p_flag |= P_CONTROLT;
  583         SESS_UNLOCK(p1->p_session);
  584         if (flags & RFPPWAIT)
  585                 p2->p_flag |= P_PPWAIT;
  586 
  587         p2->p_pgrp = p1->p_pgrp;
  588         LIST_INSERT_AFTER(p1, p2, p_pglist);
  589         PGRP_UNLOCK(p1->p_pgrp);
  590         LIST_INIT(&p2->p_children);
  591 
  592         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  593 
  594 #ifdef KTRACE
  595         /*
  596          * Copy traceflag and tracefile if enabled.
  597          */
  598         mtx_lock(&ktrace_mtx);
  599         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  600         if (p1->p_traceflag & KTRFAC_INHERIT) {
  601                 p2->p_traceflag = p1->p_traceflag;
  602                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  603                         VREF(p2->p_tracevp);
  604                         KASSERT(p1->p_tracecred != NULL,
  605                             ("ktrace vnode with no cred"));
  606                         p2->p_tracecred = crhold(p1->p_tracecred);
  607                 }
  608         }
  609         mtx_unlock(&ktrace_mtx);
  610 #endif
  611 
  612         /*
  613          * If PF_FORK is set, the child process inherits the
  614          * procfs ioctl flags from its parent.
  615          */
  616         if (p1->p_pfsflags & PF_FORK) {
  617                 p2->p_stops = p1->p_stops;
  618                 p2->p_pfsflags = p1->p_pfsflags;
  619         }
  620 
  621         /*
  622          * This begins the section where we must prevent the parent
  623          * from being swapped.
  624          */
  625         _PHOLD(p1);
  626         PROC_UNLOCK(p1);
  627 
  628         /*
  629          * Attach the new process to its parent.
  630          *
  631          * If RFNOWAIT is set, the newly created process becomes a child
  632          * of init.  This effectively disassociates the child from the
  633          * parent.
  634          */
  635         if (flags & RFNOWAIT)
  636                 pptr = initproc;
  637         else
  638                 pptr = p1;
  639         p2->p_pptr = pptr;
  640         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  641         sx_xunlock(&proctree_lock);
  642 
  643         /* Inform accounting that we have forked. */
  644         p2->p_acflag = AFORK;
  645         PROC_UNLOCK(p2);
  646 
  647         /*
  648          * Finish creating the child process.  It will return via a different
  649          * execution path later.  (ie: directly into user mode)
  650          */
  651         vm_forkproc(td, p2, td2, flags);
  652 
  653         if (flags == (RFFDG | RFPROC)) {
  654                 atomic_add_int(&cnt.v_forks, 1);
  655                 atomic_add_int(&cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  656                     p2->p_vmspace->vm_ssize);
  657         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  658                 atomic_add_int(&cnt.v_vforks, 1);
  659                 atomic_add_int(&cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  660                     p2->p_vmspace->vm_ssize);
  661         } else if (p1 == &proc0) {
  662                 atomic_add_int(&cnt.v_kthreads, 1);
  663                 atomic_add_int(&cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  664                     p2->p_vmspace->vm_ssize);
  665         } else {
  666                 atomic_add_int(&cnt.v_rforks, 1);
  667                 atomic_add_int(&cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  668                     p2->p_vmspace->vm_ssize);
  669         }
  670 
  671         /*
  672          * Both processes are set up, now check if any loadable modules want
  673          * to adjust anything.
  674          *   What if they have an error? XXX
  675          */
  676         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  677 
  678         /*
  679          * Set the child start time and mark the process as being complete.
  680          */
  681         microuptime(&p2->p_stats->p_start);
  682         mtx_lock_spin(&sched_lock);
  683         p2->p_state = PRS_NORMAL;
  684 
  685         /*
  686          * If RFSTOPPED not requested, make child runnable and add to
  687          * run queue.
  688          */
  689         if ((flags & RFSTOPPED) == 0) {
  690                 TD_SET_CAN_RUN(td2);
  691                 setrunqueue(td2, SRQ_BORING);
  692         }
  693         mtx_unlock_spin(&sched_lock);
  694 
  695         /*
  696          * Now can be swapped.
  697          */
  698         PROC_LOCK(p1);
  699         _PRELE(p1);
  700 
  701         /*
  702          * Tell any interested parties about the new process.
  703          */
  704         KNOTE_LOCKED(&p1->p_klist, NOTE_FORK | p2->p_pid);
  705 
  706         PROC_UNLOCK(p1);
  707 
  708         /*
  709          * Preserve synchronization semantics of vfork.  If waiting for
  710          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  711          * proc (in case of exit).
  712          */
  713         PROC_LOCK(p2);
  714         while (p2->p_flag & P_PPWAIT)
  715                 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
  716         PROC_UNLOCK(p2);
  717 
  718         /*
  719          * If other threads are waiting, let them continue now.
  720          */
  721         if (p1->p_flag & P_HADTHREADS) {
  722                 PROC_LOCK(p1);
  723                 thread_single_end();
  724                 PROC_UNLOCK(p1);
  725         }
  726 
  727         /*
  728          * Return child proc pointer to parent.
  729          */
  730         *procp = p2;
  731         return (0);
  732 fail:
  733         sx_sunlock(&proctree_lock);
  734         if (ppsratecheck(&lastfail, &curfail, 1))
  735                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  736                         uid);
  737         sx_xunlock(&allproc_lock);
  738 #ifdef MAC
  739         mac_destroy_proc(newproc);
  740 #endif
  741         uma_zfree(proc_zone, newproc);
  742         if (p1->p_flag & P_HADTHREADS) {
  743                 PROC_LOCK(p1);
  744                 thread_single_end();
  745                 PROC_UNLOCK(p1);
  746         }
  747         tsleep(&forksleep, PUSER, "fork", hz / 2);
  748         return (error);
  749 }
  750 
  751 /*
  752  * Handle the return of a child process from fork1().  This function
  753  * is called from the MD fork_trampoline() entry point.
  754  */
  755 void
  756 fork_exit(callout, arg, frame)
  757         void (*callout)(void *, struct trapframe *);
  758         void *arg;
  759         struct trapframe *frame;
  760 {
  761         struct proc *p;
  762         struct thread *td;
  763 
  764         /*
  765          * Finish setting up thread glue so that it begins execution in a
  766          * non-nested critical section with sched_lock held but not recursed.
  767          */
  768         td = curthread;
  769         p = td->td_proc;
  770         td->td_oncpu = PCPU_GET(cpuid);
  771         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  772 
  773         sched_lock.mtx_lock = (uintptr_t)td;
  774         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  775         cpu_critical_fork_exit();
  776         CTR4(KTR_PROC, "fork_exit: new thread %p (kse %p, pid %d, %s)",
  777                 td, td->td_sched, p->p_pid, p->p_comm);
  778 
  779         /*
  780          * Processes normally resume in mi_switch() after being
  781          * cpu_switch()'ed to, but when children start up they arrive here
  782          * instead, so we must do much the same things as mi_switch() would.
  783          */
  784 
  785         if ((td = PCPU_GET(deadthread))) {
  786                 PCPU_SET(deadthread, NULL);
  787                 thread_stash(td);
  788         }
  789         td = curthread;
  790         mtx_unlock_spin(&sched_lock);
  791 
  792         /*
  793          * cpu_set_fork_handler intercepts this function call to
  794          * have this call a non-return function to stay in kernel mode.
  795          * initproc has its own fork handler, but it does return.
  796          */
  797         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  798         callout(arg, frame);
  799 
  800         /*
  801          * Check if a kernel thread misbehaved and returned from its main
  802          * function.
  803          */
  804         PROC_LOCK(p);
  805         if (p->p_flag & P_KTHREAD) {
  806                 PROC_UNLOCK(p);
  807                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  808                     p->p_comm, p->p_pid);
  809                 kthread_exit(0);
  810         }
  811         PROC_UNLOCK(p);
  812         mtx_assert(&Giant, MA_NOTOWNED);
  813 }
  814 
  815 /*
  816  * Simplified back end of syscall(), used when returning from fork()
  817  * directly into user mode.  Giant is not held on entry, and must not
  818  * be held on return.  This function is passed in to fork_exit() as the
  819  * first parameter and is called when returning to a new userland process.
  820  */
  821 void
  822 fork_return(td, frame)
  823         struct thread *td;
  824         struct trapframe *frame;
  825 {
  826 
  827         userret(td, frame, 0);
  828 #ifdef KTRACE
  829         if (KTRPOINT(td, KTR_SYSRET))
  830                 ktrsysret(SYS_fork, 0, 0);
  831 #endif
  832         mtx_assert(&Giant, MA_NOTOWNED);
  833 }

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